1. Field of Invention
The present invention relates to a piezo-electric resonator having a piezo-electric resonator element provided in a housing, and a manufacturing method thereof.
2. Description of Related Art
There has recently been a remarkable tendency directed toward a smaller and thinner size of mobile communication devices such as an HDD (hard disk drive), a mobile computer, and compact information devices such as an IC card, a portable telephone, car telephone and a paging system. Achievement of a smaller and thinner size is also demanded for piezo-electric devices such as a piezo-electric resonator used in these communication devices. There is simultaneously a requirement for a surface mounting type piezo-electric resonator capable of being mounted on both sides of a circuit board of the device.
An example of a conventional piezo-electric resonator will therefore be described with reference to a low/medium frequency quartz resonator represented by configuration diagrams shown in FIGS. 25(a) and 25(b) using a tuning fork type quartz resonator as the piezo-electric resonator element. The low/medium frequency quartz resonator having a frequency of 32.768 kHz, a typical frequency for a watch, or of from several ten kHz to several hundred kHz, used for an IC card or a pager.
In the conventional configuration of the quartz resonator shown in FIGS. 25(a) and 25(b), a quartz resonator element 201 formed from a quartz substrate and having a metal driving electrode formed on the surface thereof is mount-connected with a conductive adhesive to a pedestal of a base 202 formed with a ceramic laminated substrate, and is sealed by a lid 203 formed of a transparent glass material in a vacuum. After seating, the resonator element is trimmed through the glass lid 203 with a laser or the like to adjust the frequency.
The above-mentioned piezo-electric resonator has a housing composed of a three-layer ceramic base and a glass lid, and is vacuum-sealed. The lid is made of a glass material such as high-quality borosilicate glass so as to permit adjustment of the frequency after sealing.
However, the glass lid requires a high material cost and also a high cost for cutting the lid from a glass substrate into a rectangular shape of the lid at a high accuracy, resulting in a high cost of the piezo-electric resonator. Fine dust produced from the glass lid exerts an adverse effect on properties of the quartz resonator. Further, the base consisting of a three-layer ceramic substrate, and air-tightness between laminated layers poses a problem, which causes deterioration of properties of the resonator element that requires keeping a high vacuum.